Technical Field
The present invention relates to a method of making a nanocomposite of graphene dispersed in poly(vinyl alcohol).
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Poly(vinyl alcohol) (PVA), being a hydrophilic and biodegradable polymer, has been used in innumerable applications. PVA as a ‘green polymer’ provides a unique opportunity for comparative studies in relation to other organic polymers. See V. Goodship et al., Polyvinyl alcohol: materials, processing and applications, Smithers Rupra Press, 2009; N. Georgieva, et al., Mater Lett 88 (2012) 19-22; J. Wang, et al., Polym Int 60 (2011) 816-822; and P. Structures, “Polymer Structures,” pp. 489-522, 1983, PVA nanocomposites with improved properties such as an increase in percent crystallinity, thermal stability, electrical/thermal conductivity, and mechanical strength have been reported. See H. Gleiter, “Materials with ultrafine microstructures: Retrospectives and perspectives.” Nanostructured Mater. 1 (1992) 1-19; R. Surudžić, et al., J. Ind. Eng. Chem. 34 (2016) 250-257; J. Jose, et al., Starch/Staerke, 67 (2015) 147-153; P. A. Sreekumat, et al., J. Appl. Polym. Sci. 123 (2012) 135-142; J. Jose, et al., Polym Bull. 71 (2014) 2787-2802; and M. Zubair, et al., Surf. Interface Anal., 46 (2014) 630-639—each incorporated herein by reference in its entirety. In the nano-filler family, carbon-containing nano-fillers, such as graphene and carbon nanotubes (CNTs), have acquired a huge attraction and interest among researchers. These nano-fillers possess remarkable properties like mechanical strength, thermal stability, electrical conductance, and a capability of being chemically functionalized. See M. Zubair, et al., Surf. Interface Anal., 46 (2014) 630-639—incorporated herein by reference in its entirety. Graphene has been in the spotlight in the nanotechnology field since 2004 because of its unprecedented properties. See K. K. Sadasivuni, et al., Graphene-Based Polymer Nanocomposites in Electronics, Springer, 2015; K. S. Novoselov, et al., Science 306 (2004) 666-9; and V. Dhand, et al., J. Nanometer, 2013 (2013) 763953—each incorporated herein by reference in its entirety. Graphene incorporated into a polymer matrix creates an extraordinary combination of thermal, mechanical and electrical properties as compared to other materials. See S. Park, et al., Nat. Nanotechnol. 4 (2009) 217-224; D. Li, et al., Nat. Nanotechnol., 3 (2008) 101-105; and A. K. Geim. Science 324 (2009) 1530-4—each incorporated herein by reference in its entirety. Improved mechanical, electrical and thermal properties of PVA nanocomposite with graphene incorporation have been reported. See J. Guo, et al., Compos. Part B Eng. 42 (2011) 2130-2135; G. W. Jeon, et al., Compos. Part B Eng. 43 (2012) 3412-3418; and J. Jose, et al., J. Appl. Polym. Sci., 132 (2015) 1-8—each incorporated herein by reference in its entirety.
Nanocomposite crystallinity and electrical properties are of great interest and are furthermore tunable with different types of fillers. Crystallinity is a measure of the structural order of a solid material. A nanocomposite's crystallinity can strongly influence its properties, such as density, diffusion, hardness, stiffness, melting point, tensile strength, and modulus. Extrinsically conductive nanocomposites have gained the attention of researchers because of their applications in electronic and electrical appliances such as sensors, electromagnetic interference shielding materials, capacitors, electrostatic discharge materials, etc. Sea S. Shang, et al., Compos. Sci. Technol 69 (2009) 1156-1159 and M. Rahaman, et al., Adv. Mater. Res. 123, (2010) 447-450—each incorporated herein by reference in its entirety. Electrically conductive PVA nanocomposites with improved electromagnetic interference shielding (EMI) and mechanical strength have also been investigated. See J.-H. Lin, et al., Macromol. Mater. Eng. 301 (2016) 199-211 and K. Fujimori, et al., J. Nanosci. Nanotechnol. 13 (2013) 1759-64—each incorporated herein by reference in its entirety. Certain electronics generate electromagnetic pollution in the form of stray radiation. Electromagnetic interference shielding materials (EMI SE) are of great concern to prevent equipment from emitting this unwanted radiation into the surrounding environment. Usually, metals are candidates for EMI shielding due to the reflection of electromagnetic radiation from their electron-rich surface. However, problems related to metals such as high density, low flexibility, processing requirements, and corrosion make them less preferable as EMI shielding materials. Thus, the use of extrinsically conductive polymer nanocomposites have been gaining interest for EMI shielding due to their easy manufacturing, their light weight, their corrosion resistance, and their low cost. See S. Wen et al., J. Mater. Sci. 40 (2005) 3897-3903 and N. C. Das et al., J. Mater. Sci. 43 (2008) 1920-1925—each incorporated herein by reference in its entirety. Many studies have been done to investigate the electromagnetic interference shielding of different polymers with graphene. See N. Georgieva, et al., Mater Lett 88 (2012) 19-22 and J. Liang, et al., Carbon 41 (2009) 922-925—each incorporated herein by reference in its entirety. The EMI SE of a nanocomposite depends on the nanocomposite's aspect ratio, intrinsic conductivity, and dielectric constant of its filler. See M. B. Bryning, et al., Adv. Mater. 17 (2005) 1186-1191—incorporated herein by reference in its entirety.
Solution casting techniques have been widely used for polymer nanocomposite preparation. However, the strong interaction between graphene sheets makes them difficult to disperse homogeneously in a polymer matrix. The demanding objective in the development of the nanocomposite is to attain fully dispersed and effective interaction of the filler with the polymer matrix. Many studies have been conducted on the functionalization of the nano-filler, small chain insinuation, and peroxide addition during melt-mixing. See L. Feng, et al., Nano Res. 8 (2015) 887-899; D. Banerjee, et al., Macromol. Res. 20 (2012) 1021-1028; G. Wu et al., Polym. Degrad. Stab. 95 (2010) 1449-1455; and D. Mcintosh, et al., J. Phys. Chem. C 111 (2007) 1592-1600—each incorporated herein by reference in its entirety.
Researchers are still trying to find out an environmentally friendly technique to acquire better interaction between the polymer matrix and the nano-filler. The irradiation of a polymer nanocomposite is considered as a useful technique to improve the structural, thermal, electrical, and mechanical properties by inducing crosslinking and/or degradation. The change in properties of a polymer under the effect of radiation depends on whether the polymer chains undergo crosslinking or chain-scission. Radiation can cause both cross-linking and chain-scission, depending on the radiation power, chemical structure, crystallite size, and the environment. See Miller A. A. Ann N Y Acad Sci 82 (1959) 774-781—incorporated herein by reference in its entirety. The degradation of PVA by irradiation has been studied by gamma rays. See S. Raghu, et al., Radiat. Phys. Chem. 98 (2014) 124-131; S. J. Zhang, et al., Water Res. 38 (2004) 309-316; and H. L. Chia, et al., J. Polym. Sci. Part A Polym. Chem. 34 (1996) 2087-2094—each incorporated herein by reference in its entirety. Microwave radiation has a strong and rapid penetration power with a significant effect on polar compounds and has been proven to be an economical, fast, and green technique for the preparation of polymer nanocomposites. Studies have scrutinized the role of microwave irradiation in graphene-polymer interaction. See M. Zubair, et al., Surf. Interface Anal. 46 (2014) 630-639; M. Zubair, et al., Thermochim. Acta 633 (2016) 48-55; D. F. Stein, Microwave Processing of Materials, Committee on Microwave Processing of Materials, National Materials Advisory Board, 1994; M. A. Al-Harthi, Polym. Compos. 35 (2014) 2036-2042; M. Zubair, et al., Compos. Interfaces 22 (2015) 595-610; and T. K. B. S., et al., Polymer 55 (2014) 3614-3627—each incorporated herein by reference in its entirety.
In view of the foregoing, one objective of the present invention is to provide a method of making microwave irradiated PVA/graphene nanocomposites which show increased crystallinity, electrical conductivity, and electromagnetic interference shielding effectiveness as compared to non-irradiated samples. These PVA/graphene nanocomposites may be made using a solution casting technique, and may be characterized by FTIR, Raman spectroscopy, XRD, SEM, electrical conductivity, and electromagnetic shielding.